"Otherwise, the rot grubs will burrow to the heart and kill their host in 1-3 turns."
Advanced Dungeons & Dragons Monster Manual, p. 83.
One to three turns. That's 10-30 minutes. That is not a lot of time to get rid of those rot grubs... but it's a hell of a sight better than 1-3 minutes (1-3 rounds) would be. In classic D&D, turns and rounds are different. This is an easy distinction to overlook, but paying attention to it could make all the difference in the world to that greedy adventurer who's been digging through offal in search of treasure (yes, even though he kind of deserves the bit of trouble he's in).
I love the 10 minute game turn in D&D as much as I love the combat round. But my impression is that it isn't one of the most beloved distinctions in the game. I should probably start by admitting that I never paid much attention to the difference between rounds and turns myself when I first learned the game as a kid, even though I learned from one of the best versions of D&D for taking turns seriously -- Mentzer's BECMI. It was only two years ago, when I first started playing classic D&D again, that I first started actually seeing how much the turn/round distinction can add to the rhythm of play, and I couldn't believe what I'd been missing.
Turns are the rhythm of dungeon adventuring that underlies movement through the dungeon, dwindling torches, decisions about when (and what) to spend time on a search, trap finding, spell durations, and decisions about when to take time to rest. And it is a foreboding rhythm as well -- the drumbeat of passing turns heralds wandering monster checks. Wandering monsters are checked once per turn in OD&D ("Underworld & Wilderness Adventures," p. 10), once every three turns in Holmes Basic (also p. 10), once every second turn in B/X (Basic Rulebook, p. B53), BECMI (Basic Set, DM's Rulebook, p. 3 and p.48), RC (p. 29), at the DM's discretion in AD&D (AD&D1, p. 38), and once per hour in AD&D2, with a note that dangerous regions of the dungeon might require checks as often as, yes, once per turn (AD&D2, DMG, p. 101).
Different versions of D&D emphasize the distinction to varying degrees, with the B/X, BECMI, RC line marking its strongest showing. But throughout classic D&D, it's there. I like to use it and make sure the players know that I'm using it. By setting out a few clear benchmarks for how long certain adventuring and exploring actions take, players have to weigh carefully how they spend there time. Is it worth checking every 10' square for traps when wandering monsters are about? How much time do you really want to put into searching this room thoroughly? If you go much deeper into the dungeon, will you have enough torches left to get back out?
Turns give structure to an otherwise unstructured activity (moving through and exploring the dungeon), and I can see that it's an activity that DMs and players have apparently tended to approach more loosely. For all Gary Gygax's admonitions about the importance of timekeeping both outside and inside the dungeon (pp. 37-38 of the DMG), the turn system isn't given the prominence in AD&D that it has in the Basic lines, nor is it integrated as tightly with other sub-systems. By AD&D 2nd edition, turns are mentioned only occasionally in the game text. And they're gone for good in 3e (and so, of course, 4e).
I'd be interested in hearing whether other people have made much use of the round versus turn distinction, and with what editions. The B/X -> BECMI -> RC line has turns built into so many of the spell durations (Sleep lasts 4d4 turns, Hold Portal 2d6 turns, Detect Magic 2 turns) that I assume a lot of people kept them alive there. But I'm very curious about how widely people have used turns to track time, movement, and searching in the dungeon, where I find them an invaluable addition to the game.